It is known that after operation of a gas turbine the rotor is driven at low speed in order to cool down quicker the gas turbine which is heated as a result of the operation. By means of the rotation of the rotor and the rotor blades which are arranged therein, cool ambient air is pumped through the flow passage of the compressor, through the combustion chamber and through the turbine unit. During the throughflow of air, this absorbs the heat which is stored in the gas turbine, i.e. in the casing and in the rotor, and transports it away. As a result of this, the gas turbine cools down quicker so that service or maintenance operations, as the case may be, can be started at any early stage because it is a general desire to reduce the downtimes of a gas turbine.
Furthermore, US 2003/35714 A1 discloses a method for cooling a turbine unit after operation of the turbine. In this case, cooling air is injected directly into the turbine inflow region, via the cooling system which is used during operation, in order to avoid heat accumulations and to avoid an overheating of the turbine after shutting down the turbine. A method similar to this is also known from U.S. Pat. No. 3,903,691.
Moreover, a cooling system for a gas turbine is known from U.S. Pat. No. 4,338,780 and from US 2004/88998 A1, in which, for cooling air cooling, water is injected into the compressed air flow which is already made available by the compressor for cooling.